Golf ball trajectory prediction method, golf ball trajectory prediction apparatus, and golf club selection method

ABSTRACT

A golf ball trajectory prediction method that can predict the trajectory of a golf ball with high accuracy is provided. The golf ball trajectory prediction method includes: a swing measurement step of measuring a golfer&#39;s swing using a test golf club; a head behavior prediction step of predicting a behavior of a head of a target golf club when using the target golf club, with a measurement value of the swing measured in the swing measurement step as input; a ball initial behavior calculation step of calculating an initial behavior of a golf ball after colliding with the head of the golf club, based on the behavior of the head predicted in the head behavior prediction step; and a ball trajectory prediction step of predicting a trajectory of the golf ball, from the initial behavior of the golf ball calculated in the ball initial behavior calculation step.

TECHNICAL FIELD

The disclosure relates to a golf ball trajectory prediction method, agolf ball trajectory prediction apparatus, and a golf club selectionmethod.

BACKGROUND

Techniques of predicting, through calculation, the golf swing, the stateof collision between a golf club and a golf ball, the trajectory of agolf ball, etc. are in high demand. These prediction techniques areparticularly important upon golf club fitting (selection, adjustment,custom-making).

In golf club fitting, typically, a golfer's swing using a club formeasurement is measured to predict, based on the measured swing data,the state of golf swing when using each of various clubs, and thepredicted golf swing state is used as an index of fitting.

For example, Patent Literature (PTL) 1 discloses a technique ofanalyzing the golf swing based on information including the speed of thegrip end of a golf club in the impact state immediately before hitting agolf ball, and selecting an optimal golf club for the golf swing.

Ideal golf club fitting is based on the trajectory (carry distance anddirection) of a golf ball after colliding with a golf club. Thus, asuitable golf club can be selected according to the ball's carrydistance and direction desired by the golfer.

CITATION LIST Patent Literature

PTL 1: JP 4184363 B2

SUMMARY

It could therefore be helpful to provide a golf ball trajectoryprediction method and golf ball trajectory prediction apparatus that canpredict the trajectory of a golf ball with high accuracy, and a golfclub selection method that can select a suitable golf club.

We thus provide the following:

A golf ball trajectory prediction method according to the disclosureincludes: a swing measurement step of measuring a golfer's swing using atest golf club; a head behavior prediction step of predicting a behaviorof a head of a target golf club when using the target golf club, with ameasurement value of the swing measured in the swing measurement step asinput; a ball initial behavior calculation step of calculating aninitial behavior of a golf ball after colliding with the head of thegolf club, based on the behavior of the head predicted in the headbehavior prediction step; and a ball trajectory prediction step ofpredicting a trajectory of the golf ball, from the initial behavior ofthe golf ball calculated in the ball initial behavior calculation step.

With such a method, the trajectory of the golf ball can be predictedwith high accuracy.

Preferably, in the ball initial behavior calculation step, the initialbehavior of the golf ball after colliding with the head of the golf clubis calculated using a regression equation derived beforehand fromcollision analysis between the head of the golf club and the golf ball,with a prediction value of the behavior of the head predicted in thehead behavior prediction step as input. In this way, the trajectory ofthe golf ball can be predicted accurately in a shorter time.

Preferably, in the ball initial behavior calculation step, the initialbehavior of the golf ball after colliding with the head of the golf clubis calculated by collision analysis based on a finite element method,with a prediction value of the behavior of the head predicted in thehead behavior prediction step as input. In this way, the trajectory ofthe golf ball can be predicted more accurately.

Preferably, in the swing measurement step, a meeting rate of the golfball in the swing is further measured, and in the head behaviorprediction step, only a swing with a meeting rate not less than apredetermined threshold is used as input, from among the swing measuredin the swing measurement step. More preferably, the meeting rate is aninitial speed of the launched golf ball with respect to a speed of thehead of the golf club upon impact. In this way, the trajectory of thegolf ball can be predicted more accurately.

Preferably, in the swing measurement step, the initial behavior of thegolf ball in the swing is further measured, and the initial behavior ofthe golf ball measured in the swing measurement step and the initialbehavior of the golf ball calculated in the ball initial behaviorcalculation step are compared with each other, to correct a result ofthe calculation that is based on the prediction value of the behavior ofthe head. In this way, the trajectory of the golf ball can be predictedmore accurately.

Preferably, in the swing measurement step, the initial behavior of thegolf ball in the swing is further measured, and the initial behavior ofthe golf ball measured in the swing measurement step and the initialbehavior of the golf ball calculated in the ball initial behaviorcalculation step are compared with each other, to correct a resultcalculated from the regression equation. In this way, the trajectory ofthe golf ball can be predicted more accurately.

Preferably, the initial behavior of the golf ball includes an initialspeed, a launch angle, and a spin rate of the golf ball after collidingwith the head of the golf club. In this way, the trajectory of the golfball can be predicted more accurately.

Preferably, the regression equation is derived from motion analysisbased on a finite element method. In this way, the trajectory of thegolf ball can be predicted more accurately.

A golf ball trajectory prediction apparatus according to the disclosure:measures a golfer's swing using a test golf club; predicts a behavior ofa head of a target golf club when using the target golf club, with themeasured swing as input; calculates an initial behavior of a golf ballafter colliding with the head of the golf club, based on a predictionvalue of the behavior of the head; and predicts a trajectory of the golfball, from the calculated initial behavior of the golf ball.

With such a structure, the trajectory of the golf ball can be predictedwith high accuracy.

Preferably, the initial behavior of the golf ball after colliding withthe head of the golf club is calculated using a regression equationderived beforehand from collision analysis between the head of the golfclub and the golf ball, with the prediction value of the behavior of thehead as input. In this way, the trajectory of the golf ball can bepredicted accurately in a shorter time.

A golf club selection method according to the disclosure selects a golfclub based on a trajectory of a golf ball predicted by the golf balltrajectory prediction method according to the disclosure.

With such a method, a suitable golf club can be selected.

It is possible to provide a golf ball trajectory prediction method andgolf ball trajectory prediction apparatus that can predict thetrajectory of a golf ball with high accuracy, and a golf club selectionmethod that can select a suitable golf club.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a flowchart illustrating one of the embodiments of a golf balltrajectory prediction method according to the disclosure; and

FIG. 2 is a flowchart illustrating another one of the embodiments of thegolf ball trajectory prediction method according to the disclosure.

DETAILED DESCRIPTION

Our methods and apparatuses are described in detail below, by way ofembodiments. FIG. 1 and FIG. 2 each illustrate a different one of theembodiments of a golf ball trajectory prediction method according to thedisclosure.

(Golf Ball Trajectory Prediction Method)

One of the embodiments of a golf ball trajectory prediction methodaccording to the disclosure is described below.

As illustrated in FIG. 1 and FIG. 2, the disclosed golf ball trajectoryprediction method includes: a swing measurement step of measuring agolfer's swing using a test golf club (FIG. 1(a) and FIG. 2(a)); a headbehavior prediction step of predicting a behavior of a head of a targetgolf club when using the target golf club, with a measurement value ofthe swing measured in the swing measurement step as input (FIG. 1(b) andFIG. 2(b)); a ball initial behavior calculation step of calculating aninitial behavior of a golf ball after colliding with the head of thegolf club, based on the behavior of the head predicted in the headbehavior prediction step (FIG. 1(c) and FIG. 2(c)); and a balltrajectory prediction step of predicting a trajectory of the golf ball,from the initial behavior of the golf ball calculated in the ballinitial behavior calculation step (FIG. 1(d) and FIG. 2(d)).

With such a method, the trajectory of the golf ball can be predictedwith high accuracy.

The most important information when a golfer selects a golf club is theball trajectory, i.e. the flight path that the ball follows whenlaunched with the club. The ball trajectory can be theoreticallycalculated from the initial behavior of the golf ball immediately afterthe launch. It is therefore important to recognize the initial behaviorof the golf ball, in order to obtain the trajectory information.

The initial behavior of the ball is typically recognized by actuallytrial-hitting the ball with a target golf club and measuring the initialbehavior of the ball immediately after the launch by a measuringinstrument. However, given that the number of clubs a golfer canactually trial-hit is physically and temporally limited and also aperson's swing varies, it is difficult to compare many clubs under thesame conditions.

Hence, the following technique is employed: The use of each of aplurality of target clubs is calculated on a computer by a computersimulation, and an optimal club is selected from many target clubs byusing the calculation results as fitting indices. The computersimulation includes two steps: a swing simulation step (head behaviorprediction step) of calculating the behavior of the head with theperson's swing feature as input; and a collision simulation step (ballinitial behavior calculation step) of predicting the initial behavior ofthe ball from the behavior of the head upon impact (approach condition).

In view of the above, the disclosed technique calculates the initialbehavior of the golf ball after colliding with the head based on, forexample, the finite element method or a regression equation obtainedfrom the finite element method. This enables accurate prediction of theinitial behavior of the golf ball, and as a result enables accurateprediction of the trajectory of the golf ball.

Swing Measurement Step

The disclosed golf ball trajectory prediction method includes a swingmeasurement step of measuring a golfer's swing using a test golf club,as illustrated in FIG. 1(a) and FIG. 2(a).

The swing measurement step is a step of measuring, by a given measuringinstrument, input data for performing a swing simulation.

The test golf club is used for the golfer's swing, as mentioned above.Even in the case where the conditions of the golf club or golf ball arechanged, the prediction can be made by calculation. This reduces thetime and labor required to change the golf club, the number of swings,and the like.

The test golf club is not particularly limited as long as its physicalcharacteristics are known. A golf club prepared by the golfer may beused as the test golf club. In such a case, it is desirable to perform aswing simulation that reflects the physical characteristics of the golfclub prepared by the golfer.

The measurement value of the swing obtained in the swing measurementstep is not particularly limited as long as a measurement method formeasuring the golfer's swing feature is used.

For example, the measurement value of the swing is preferably theacceleration data or three-dimensional coordinate data of the gripportion acquired using an accelerometer, motion capture, or the like.

The measurement conditions of the accelerometer or motion capture arenot particularly limited, and may be adjusted as appropriate to acquiredesired swing data.

In the swing measurement step, preferably, the initial behavior of thegolf ball launched in the swing is further measured (FIG. 1(e) and FIG.2(e)). The measured initial behavior of the golf ball can be used tocorrect the calculation result obtained based on the below-mentionedregression equation. The measurement of the initial behavior of the golfball in the swing measurement step is performed for each golfer, toacquire data for correction as described later. Accordingly, the initialbehavior of the golf ball need not be measured again after thecorrection.

Measurement of Meeting Rate and Comparison with Threshold

The disclosed golf ball trajectory prediction method further measuresthe meeting rate in the swing measurement and determines whether or notthe meeting rate is not less than a predetermined threshold, asillustrated in FIG. 1(h). Only each swing with a meeting rate not lessthan the threshold is preferably used as input in the below-mentionedhead behavior prediction step.

In the case where the head of the golf club and the ball collide in anideal form, the meeting rate is high. The meeting rate can thus be usedas an index of such ideal collision. By using only each swingmeasurement with a meeting rate not less than the threshold as input,any swing measurements corresponding to mishits are excluded, so thatthe initial behavior of the golf ball can be calculated more accurately.For example, in the case of measuring a driver swing using TrackManmanufactured by TrackMan A/S, the threshold of the meeting rate may be1.4 or more and, if the golfer is capable of considerably accuratecollision, 1.45 or more. A meeting rate not less than 1.4 may not beable to be obtained depending on the measuring instrument or the clubused. In such a case, the threshold is desirably readjusted asappropriate.

The meeting rate mentioned here is the initial speed of the launchedball with respect to the speed of the head upon impact ((initial ballspeed)/(head speed)). The method of acquiring the meeting rate is notparticularly limited, and the meeting rate may be acquired by measuringeach of the initial speed of the launched ball and the head speed uponimpact by a commercially available measuring instrument or the like.

Head Behavior Prediction Step

The disclosed golf ball trajectory prediction method includes, after theabove-mentioned swing measurement step, a step (head behavior predictionstep) of predicting the behavior of the head when using a target golfclub with the measured swing as input, as illustrated in FIG. 1(b) andFIG. 2(b).

The head behavior prediction step is a step of predicting, throughcalculation from the measured swing, the behavior of the head whichserves as an input value (explanatory variable) in the calculation usingthe regression equation or the like in the below-mentioned ball initialbehavior calculation step (FIG. 1(c) and FIG. 2(c)).

The behavior of the head mentioned here is the approach condition of thehead immediately before impacting the golf ball. For example, thebehavior of the head includes the attitude angle (θ) and the magnitudeof the speed vector (v) of the head of the golf club. Any othernecessary parameter(s) may be predicted as appropriate, as an inputvalue to the below-mentioned regression equation.

The behavior of the head is predicted in a state where information aboutthe shaft and head of the target golf club is incorporated in themeasured swing of the test golf club, to enable prediction of thebehavior of the head when using the target golf club. The informationabout the shaft and head of the target golf club includes the bendingrigidity (EI), torsional rigidity, weight, length, etc. of the shaft ofthe golf club, and the center of gravity, loft angle, lie angle, etc. ofthe head of the golf club. A golf club model reflecting theseinformation is used for the calculation.

The target golf club mentioned here is a golf club that is subject togolf ball trajectory prediction.

The behavior of the head can be predicted by calculation using acomputer, with the measured swing as an input value. For example, amethod of simulating the behavior of the head with the measured swing asan input value to calculate the attitude angle (θ) and speed vector (v)of the head is available.

Ball Initial Behavior Calculation Step

The disclosed golf ball trajectory prediction method includes, after theabove-mentioned head behavior prediction step, a step (ball initialbehavior calculation step) of calculating the initial behavior of thegolf ball after colliding with the head of the golf club based on thebehavior of the head predicted in the head behavior prediction step, asillustrated in FIG. 1(c) and FIG. 2(c).

The ball initial behavior calculation step is a step of calculating theinitial behavior of the golf ball after colliding with the head bymotion analysis based on the finite element method or calculation of theregression equation prepared beforehand, etc., and can determine theaccurate initial behavior of the golf ball.

The initial behavior of the golf ball is the state of the golf ballafter colliding with the head of the golf club, and the trajectory ofthe golf ball is predicted based on the initial behavior of the golfball. The initial behavior of the golf ball is not particularly limited,and may be any of various parameters. The initial behavior of the golfball preferably includes the initial speed, launch angle, and spin rateof the golf ball after colliding with the head of the golf club. Theseparameters are factors that significantly affect the trajectory of thegolf ball. By using these parameters as the initial behavior, thetrajectory of the golf ball can be predicted with high accuracy.

The calculation of the initial behavior of the golf ball based on theprediction value of the behavior of the head of the golf club ispreferably performed as follows: The initial behavior of the golf ballafter colliding with the head of the golf club is calculated using aregression equation derived beforehand from collision analysis betweenthe head of the golf club and the golf ball, with the prediction valueof the behavior of the head predicted in the head behavior predictionstep as input, as illustrated in FIG. 2(c).

In the case of calculating the initial behavior of the golf ball afterthe launch by a collision simulation based on the finite element methodor the like, the simulation using existing computer resources takes longtime. In view of this, the behavior of the ball after the collision iscalculated beforehand by the finite element method or the like withvarious head behaviors as input to derive the regression equation forthe behavior of the head and the initial behavior of the ball, and theinitial behavior of the golf ball is calculated using the regressionequation. This significantly reduces the calculation time, as comparedwith the case of performing the simulation based on the finite elementmethod or the like. Approximating such complex calculation by theregression equation typically leads to lower prediction accuracy. Bysetting the threshold of the meeting rate, however, the calculation canbe limited within the range where the regression equation appliesefficiently.

The regression equation is preferably an equation generated based on theresult of collision analysis by the finite element method or the likefor the behavior of the head of the golf club with various approachconditions prepared beforehand. The collision analysis technique is notparticularly limited, and may be any known technique as appropriate.

The regression equation is not particularly limited as long as theintended initial behavior of the golf ball can be calculated with theprediction value of the behavior of the head as input. To predict theinitial behavior of the golf ball with higher accuracy, the regressionequation is preferably derived from motion analysis based on the finiteelement method.

The collision analysis mentioned here is the analysis of motion beforeand after the collision between the head of the golf club and the ball.

The regression equation differs depending on the head and the ball. Inthe case where the characteristics (e.g. loft angle, center of gravityof each head are different, the regression equation needs to be derivedfor each head.

The regression equation is, for example, the following equation (1):

Y=αX+β  (1)

where Y is the launch angle (the angle between the ball's target lineand the horizon), α is a proportionality constant (e.g. about 0.9±0.1),X is the angle between the face of the head and the horizon (dynamicloft), and β is a proportionality constant (e.g. about −0.3).

While the initial behavior of the golf ball is preferably calculatedusing the above-mentioned regression equation derived beforehand fromthe collision analysis between the head of the golf club and the golfball, collision analysis based on the finite element method with theprediction value of the behavior of the head as input may also be used.This enables accurate calculation of the initial behavior of the golfball, although the calculation time is longer. The collision analysismentioned here is the analysis of motion before and after the collisionbetween the head of the golf club and the ball.

The finite element method (FEM) is one of the numerical analysismethods, and can numerically find an approximate solution to ahardly-analyzable differential equation by dividing the area in whichthe equation is defined into smaller areas (elements) and approximatingthe equation in each smaller area by a common interpolation function.

When using the finite element method to predict the initial behavior ofthe golf ball, for example, a method of numerically finding the initialbehavior (e.g. the initial speed, spin rate, etc. after the collision)of the golf ball by dividing the head of the golf club which collideswith the golf ball into smaller areas and analyzing the areas isavailable.

The result of calculation using the motion analysis based on the finiteelement method or the regression equation is preferably correctedaccording to the result of comparing the calculated initial behavior ofthe golf ball and the measured initial behavior of the golf ball. Thisenhances the correctness of calculation, and enables more accurateprediction of the trajectory of the golf ball.

As illustrated in FIG. 1 and FIG. 2, the initial behavior of thelaunched golf ball is also measured (FIG. 1(e) and FIG. 2(e)) in theswing measurement step (FIG. 1(a) and FIG. 2(a)), and then the measuredinitial behavior of the golf ball and the calculated initial behavior ofthe golf ball are compared with each other (FIG. 1(f) and FIG. 2(f)) toperform the correction based on the comparison result (FIG. 1(g) andFIG. 2(g)).

The method of correcting the calculation result and the regressionequation is not particularly limited as long as it can enhance thecorrectness of calculation. To easily and reliably enhance thecorrectness of calculation, offset correction that directly adds thedifference from the measured initial behavior of the golf ball to thecalculated initial behavior of the golf ball is more preferable.

The offset correction is described in detail below.

The calculated initial behavior of the ball contains a certain amount oferror (hereafter “error X”). As various factors cause the error X, it ishard to precisely specify the cause of the error X. Examples include ameasurement error during swing measurement and a deviation from thesweet spot at impact.

When a golfer selects a club, the relative difference between clubs,that is, how the trajectory changes in the case of switching from areference club to a target club, is important. In the disclosedtechnique, the test club is used as the reference club. Hence, thedifference between the initial condition of the ball obtained throughsimulation and calculation (including the regression equation) with aclub model corresponding to the test club and the actual initialbehavior of the ball measured using the test club is determined. Thisdifference corresponds to the error X.

The difference is added to (or subtracted from) the initial behavior ofthe ball obtained through simulation and calculation for each of thevarious target clubs. By such correction, the relative difference, thatis, how the trajectory changes with respect to the actual trajectorywhen using the target club, is obtained. The easy-to-understand resultcan thus be presented to the golfer.

Ball Trajectory Prediction Step

The disclosed golf ball trajectory prediction method includes, after theabove-mentioned ball initial behavior calculation step, a step (golfball trajectory prediction step) of predicting the trajectory of thegolf ball from the initial behavior of the golf ball calculated in theball initial behavior calculation step, as illustrated in FIG. 1(d) andFIG. 2(d).

The golf ball trajectory prediction step is a step of predicting,through calculation, which trajectory the ball launched from the targetgolf club follows, based on the calculated initial behavior of the golfball. The trajectory may be visual data representing the trajectory, ornumerical data of the carry distance, horizontal deviation, launchangle, landing angle, trajectory height, etc.

The method of predicting the trajectory of the golf ball is notparticularly limited, and may be any known prediction method.

For example, a method of deriving, from the calculated initial behaviorof the golf ball, the motion component of the golf ball by computeroperation and simulating the trajectory is available.

(Golf Ball Trajectory Prediction Apparatus)

One of the embodiments of a golf ball trajectory prediction apparatusaccording to the disclosure is described below.

The disclosed golf ball trajectory prediction apparatus: measures agolfer's swing using a test golf club; predicts a behavior of a head ofa target golf club when using the target golf club, with the measuredswing as input; calculates an initial behavior of a golf ball aftercolliding with the head of the golf club, based on the prediction valueof the behavior of the head; and predicts a trajectory of the golf ball,from the calculated initial behavior of the golf ball.

With such a structure, the trajectory of the golf ball can be predictedwith high accuracy.

Preferably, the golf ball trajectory prediction apparatus furthermeasures the meeting rate in the swing measurement and uses, from amongthe measured swings, only each swing with a meeting rate not less than apredetermined threshold as input in the head behavior prediction.

The reasons for using only each swing with a meeting rate not less thanthe threshold, the suitable threshold, etc. are as described above.

The golfer's swing measurement is not particularly limited, and may beperformed using the above-mentioned accelerometer or motion capture asan example.

The meeting rate measurement is not particularly limited. For example,the meeting rate may be calculated by measuring each of the head speedupon impact and the initial speed of the launched ball using a measuringinstrument such as a high-speed camera, or measured using a commercialavailable meeting rate measuring instrument.

The head behavior prediction is not particularly limited, and may beperformed using a computer installed with commercially availablesimulation software.

The golf ball initial behavior calculation may be performed using acomputer installed with motion analysis software based on the finiteelement method or a specific regression equation.

The golf ball trajectory prediction is not particularly limited, and maybe performed using a computer installed with commercially availablesimulation software.

In the golf ball trajectory prediction apparatus, preferably, theinitial behavior of the golf ball after colliding with the head of thegolf club is calculated using a regression equation derived beforehandfrom collision analysis between the head of the golf club and the golfball, with the prediction value of the behavior of the head as input.

As mentioned earlier, the behavior of the golf ball after the collisionis calculated based on the finite element method or the like withvarious head behaviors as input to generate the regression equation forthe behavior of the head and the initial behavior of the golf ballbeforehand, and the initial behavior of the golf ball is calculatedusing the regression equation. In this way, the calculation time can besignificantly reduced as compared with the case of performing thesimulation based on the finite element method or the like.

The details of the other components in the disclosed golf balltrajectory prediction apparatus are the same as those described withregard to the disclosed golf ball trajectory prediction method.

(Golf Club Selection Method)

One of the embodiments of a golf club selection method according to thedisclosure is described below.

The disclosed golf club selection method selects a golf club based on atrajectory of a golf ball predicted by the golf ball trajectoryprediction method described above.

With such a method, a suitable golf club can be selected based on theaccurately predicted trajectory of the golf ball.

For example, the golfer can select his or her favorite club based on animage representing the predicted trajectory or prediction data of thecarry distance, launch angle, landing angle, trajectory height, etc.Moreover, the store(s) or manufacturer(s) can select and recommend anoptimal golf club to the golfer based on the predicted trajectory.

INDUSTRIAL APPLICABILITY

It is possible to provide a golf ball trajectory prediction method andgolf ball trajectory prediction apparatus that can predict thetrajectory of a golf ball with high accuracy, and a golf club selectionmethod that can select a suitable golf club.

1. A golf ball trajectory prediction method comprising: a swingmeasurement step of measuring a golfer's swing using a test golf club; ahead behavior prediction step of predicting a behavior of a head of atarget golf club when using the target golf club, with a measurementvalue of the swing measured in the swing measurement step as input; aball initial behavior calculation step of calculating an initialbehavior of a golf ball after colliding with the head of the golf club,based on the behavior of the head predicted in the head behaviorprediction step; and a ball trajectory prediction step of predicting atrajectory of the golf ball, from the initial behavior of the golf ballcalculated in the ball initial behavior calculation step.
 2. The golfball trajectory prediction method according to claim 1, wherein in theball initial behavior calculation step, the initial behavior of the golfball after colliding with the head of the golf club is calculated usinga regression equation derived beforehand from collision analysis betweenthe head of the golf club and the golf ball, with a prediction value ofthe behavior of the head predicted in the head behavior prediction stepas input.
 3. The golf ball trajectory prediction method according toclaim 1, wherein in the ball initial behavior calculation step, theinitial behavior of the golf ball after colliding with the head of thegolf club is calculated by collision analysis based on a finite elementmethod, with a prediction value of the behavior of the head predicted inthe head behavior prediction step as input.
 4. The golf ball trajectoryprediction method according to claim 1, wherein in the swing measurementstep, a meeting rate of the golf ball in the swing is further measured,and in the head behavior prediction step, only a swing with a meetingrate not less than a predetermined threshold is used as input, fromamong the swing measured in the swing measurement step.
 5. The golf balltrajectory prediction method according to claim 4, wherein the meetingrate is an initial speed of the launched golf ball with respect to aspeed of the head of the golf club upon impact.
 6. The golf balltrajectory prediction method according to claim 1, wherein in the swingmeasurement step, the initial behavior of the golf ball in the swing isfurther measured, and the initial behavior of the golf ball measured inthe swing measurement step and the initial behavior of the golf ballcalculated in the ball initial behavior calculation step are comparedwith each other, to correct a result of the calculation that is based ona prediction value of the behavior of the head.
 7. The golf balltrajectory prediction method according to claim 2, wherein in the swingmeasurement step, the initial behavior of the golf ball in the swing isfurther measured, and the initial behavior of the golf ball measured inthe swing measurement step and the initial behavior of the golf ballcalculated in the ball initial behavior calculation step are comparedwith each other, to correct a result calculated from the regressionequation.
 8. The golf ball trajectory prediction method according toclaim 1, wherein the initial behavior of the golf ball includes aninitial speed, a launch angle, and a spin rate of the golf ball aftercolliding with the head of the golf club.
 9. The golf ball trajectoryprediction method according to claim 2, wherein the regression equationis derived from motion analysis based on a finite element method.
 10. Agolf ball trajectory prediction apparatus that: measures a golfer'sswing using a test golf club; predicts a behavior of a head of a targetgolf club when using the target golf club, with the measured swing asinput; calculates an initial behavior of a golf ball after collidingwith the head of the golf club, based on a prediction value of thebehavior of the head; and predicts a trajectory of the golf ball, fromthe calculated initial behavior of the golf ball.
 11. The golf balltrajectory prediction apparatus according to claim 10, wherein theinitial behavior of the golf ball after colliding with the head of thegolf club is calculated using a regression equation derived beforehandfrom collision analysis between the head of the golf club and the golfball, with the prediction value of the behavior of the head as input.12. A golf club selection method of selecting a golf club based on atrajectory of a golf ball predicted by the golf ball trajectoryprediction method according to claim 1.